In a world that places a premium on sustainable energy production and energy conservation, the use of phase change materials (PCM) to moderate temperature and climatic conditions has made them an important commodity. Phase change materials are designed to release or absorb energy at predictable temperatures and, thereby, maintain an associated space or structure within a predetermined temperature range.
Generally, when the ambient temperature increases a solid-liquid PCM absorbs sensible heat. When the PCM reaches the temperature at which it undergoes its phase transition (i.e. the temperature at which the PCM material changes from a solid state to a liquid state), the PCM temperature stops increasing and substantially maintains a constant phase change temperature. This is an endothermic process and the PCM “absorbs” the heat being applied thereto and stores it as latent heat in the material's chemical bonds.
“Latent heat” is the heat gained by a substance during a phase change without any accompanying rise in the temperature of the substance. In essence, it is the amount of heat necessary to change a substance from the solid state to the liquid state. Once the phase change material has completely changed to a liquid state, the temperature of the (now liquid) PCM begins to rise again as the applied heat is absorbed as sensible heat.
In the reverse process, as the ambient temperature decreases the PCM drops in temperature as it releases the excess sensible heat which was absorbed beyond the phase change temperature. At the phase change temperature, the PCM returns to its solid phase releasing the latent heat back to the environment at the phase change temperature of the PCM. As before, the PCM maintains a substantially constant temperature at its phase change temperature while giving up the stored latent heat.
The heat absorption and release properties of PCM can be harnessed to store and release thermodynamic energy as required for a specific application. There is particular interest in PCM that can maintain various temperatures between −20° C. and 150° C. PCMs may be used in building materials such as walls, flooring, ceiling panels and solar heat storage systems, as well as heating, ventilating, and air conditioning (HVAC) applications. Other potential applications for PCM include: thermal energy storage, waste heat recovery, off peak power utilization, heat pump efficiency, space exploration, computer/electrical component cooling, food storage containers, and clothing and textiles.
Most current PCM is based on paraffin waxes and similar materials derived from petroleum. These materials have relatively high heats of fusion, low vapor pressure, and no phase separation. However, despite these desirable properties petroleum-based PCMs suffer from low thermal conductivity, moderate flammability, and large volume changes during phase transition. Further, materials derived from pure paraffin waxes are expensive and non-biodegradable. Pure paraffins are frequently mixed with lower grade hydrocarbons to control cost. However, the performance of the resulting hydrocarbon mix-based PCM is significantly degraded.
Only a few non-petroleum based PCMs have been seriously studied. Although fatty acids and their esters have suitable melting points and heat of fusion values, fatty acids are corrosive and are generally less efficient than petroleum-based equivalents.
The need exists for a bio-based PCM that exhibits performance qualities at least equivalent to current petroleum-based PCMs. The current invention comprises a non-corrosive oleochemical carbonate PCM with performance that is comparable to petroleum-based PCMs. The PCM of the current invention has a lower cost and is derived from renewable agricultural products and is therefore more environmentally friendly than the current petroleum-based alternative.